1. Technical Field
This invention relates generally to shaft seals, and more particularly to those including a wear sleeve.
2. Related Art
Commonly owned U.S. Pat. No. 5,676,383 to Chandler discloses a shaft seal assembly having an outer carrier which mounts in a bore of housing. The carrier has an inner flange on which a body of elastomeric material is molded. The elastomer body is configured to provide a primary sealing lip and two diverging secondary dust exclusion lips. An inner wear sleeve component mounts about a shaft for rotation therewith relative to the carrier and elastomer seal body. The primary seal runs on an outer surface of a cylindrical body of the wear sleeve and provides a barrier to the escape of fluid within the housing. The wear sleeve has an end flange that extends radially outwardly of the body and is turned axially inwardly at its free end back toward the carrier on an air side of the seal. The secondary diverging dust lips extend in close proximity to the cylindrical body and axially inward flange portion of the wear sleeve to block the entrance of debris into the seal. In order to capture the wear sleeve detachably on the elastomer body, the axially inner end of the wear sleeve is formed with a radially outwardly turned retaining flange which acts to confront the elastomer body when an axially outward force is applied to the wear sleeve to prevent the wear sleeve from becoming separated from the elastomer body. One drawback to such a seal configuration is that the primary elastomer seal lip is best suited for light duty applications, but is not well suited for use in heavy duty seal applications, such as in heavy power equipment, where the environment encountered by the seal is extremely dirty and the seal is prone to operating under dry, abrasive, hot conditions. Another drawback to such unitized seals is that the radially outward bending of the retaining flange of the wear sleeve has the effect of stressing the wear sleeve such that the outer sealing surface is no longer truly cylindrical and flat in the axial direction, but has a cylindrical dip or depression in the outer sealing surface inward from the retaining flange. While such a depression may not pose a serious problem since the line contact of the elastomer lip can readily conform to the shape of the sealing surface, such a deformity in the sealing surface may cause problems with other type of seals, such as PTFE seals which are typically bent to form an axial collar which lays down against the outer running surface of the sleeve and extends along a considerable portion of the wear sleeve running surface, including into the region which would be deformed out of shape in response to forming the inner capturing end flange of the wear sleeve. Such a lay-down type PTFE seal is shown, for example, in commonly owned U.S. Pat. No. 6,257,587. With such lay-down PTFE primary seals, the inward retaining flange formed on the wear sleeve can thus distort the running surface that the seal collar rides against, impairing its sealing effectiveness.
Another problem encountered with unitized-type oil seals is that there is presently no good way of installing them about the shaft and within a bore of the housing in a manner that precisely aligns the wear sleeve axially with respect to the carrier and seal elements of the carrier on a repeatable basis during original installation and replacement in the field. The seal assembly disclosed in the mentioned U.S. Pat. No. 5,676,383 is mounted within the bore of the housing, inset from an end face. There is no disclosure as to how the axial relationship of the wear sleeve and carrier are maintained or controlled during installation. However, this particular design may be relatively insensitive to variations in the axial positioning of the wear sleeve relative to the carrier, since the divergent dust exclusion lips are located off radially outwardly and inwardly facing surfaces of the body and axial flange portion of the wear sleeve, and not off the axially inner face of the radial end flange of the wear sleeve, such that a small variation in the location of the wear sleeve relative to the carrier does not disturb the spacing of the divergent lips relative to their neighboring radially inwardly and outwardly facing surfaces of the wear sleeve. The spacing between the divergent lips and these neighboring surfaces is considerably less than the spacing between the lips and the axially inner face of the end flange of the wear sleeve. The axial flange portion of the end flange is further of such length that axial inward displacement of the wear sleeve relative to the carrier causes the inward end of the flange portion to abut the carrier, precluding the possibility of contact of the divergent dust lips with the axially inner face of the end flange. In other words, the spacing between the radially outermost dust lip and the axially inner face of the end flange is greater than the spacing between the axial flange portion and the surface of the carrier which it confronts if the wear sleeve is displaced axially inwardly, precluding the possibility of the radially outward most dust lip from contacting the axially inner face of the end flange.
U.S. Pat. No. 5,895,052 is another example of an integrated shaft seal having a wear sleeve captured by an elastomeric body molded to a carrier by means of an outwardly bent retaining flange of the wear sleeve. Primary and two secondary lips are formed in one piece from the same elastomeric material, presenting a primary seal lip which makes line contact with the outer sealing surface of the cylindrical wear sleeve body adjacent the retaining flange. There is no disclosure as to how one installs such a seal in a way that assures the proper or desired relative axial positioning of the wear sleeve relative to the carrier in a precise, repeatable manner so as to maintain the crucial spatial relationship of the components for correct operation of the labyrinth flow path set up on the air side of the seal by the dust lips and adjacent surfaces of the wear sleeve. Accordingly, the seal assembly disclosed in U.S. Pat. No. 5,895,052 shares many of the same limitations of the seal assembly disclosed in U.S. Pat. No. 5,676,383, particularly with regard to ease of installation and axial alignment of the wear sleeve and carrier components, and distortion of the outer running surface of the wear sleeve adjacent the axially inner end of the wear sleeve due to bending deformation of the wear sleeve in order to provide a radially outwardly extending retaining flange or projection which confronts the primary seal to preclude separation of the wear sleeve from the carrier.
A seal assembly constructed according to the present invention greatly minimizes or overcomes the foregoing shortcomings of prior art seal devices.